The emergence of decreasing trends in snowfall frequency and snow depth highlights the challenges arising from shifts in snow regimes. In particular, snow-dependent southern Europe regions may be negatively impacted by such changes. Snow regimes strongly influence the water availability in reservoirs and groundwater. This study presents the world's longest series of monthly snowfall (fresh snow depth, snow days per year, days with snow on the ground) for the Parma Observatory, northern Italy (44 degrees 48 ' N and 10 degrees 19 ' E) between 1777 and 2018. These datasets were collected over the centuries using early rain gauges and recently, SIAP tipping bucket models. Sources of inhomogeneity were identified and analysed through the study of metadata and of nonparametric tests on datasets. Homogenized time series were obtained after correcting the observed snowfall data for the instruments response and localization characteristics, for the observing practices with the help of the standard normal homogeneity tests. The Buishand and the Mann-Kendall tests were further applied to check the correction and detect possible monotonic trends. Over the study period, days per year of snow decreased after the change point detected in 1897, in association with a rise in surface air temperature (including a distinct urban warming trend). In this study high numbers of snowy days per year (hereafter referred as snowfall frequency) and snow depth values during the latest phase of the LIA at Parma are consistent with a cycle of minimum solar activity, suggesting that enhanced, solar-induced blocking activity dominated, with the arrival into the Mediterranean of large cold air masses developing over Siberia and northern Europe. Over the last century, snow appears to have resonance-like characteristics as similar trends were observed over the Northern Hemisphere, where the extent of the snow cover has been reported to markedly decline in the transition spring and autumn seasons.

中文翻译：

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对世界上最长的月降雪系列的新见解（意大利北部帕尔马，1777-2018 年）

降雪频率和积雪深度下降趋势的出现凸显了降雪情况变化带来的挑战。尤其是依赖雪的南欧地区可能会受到此类变化的负面影响。雪情强烈影响水库和地下水中的可用水量。这项研究展示了意大利北部帕尔马天文台（北纬 44 度 48 分和东经 10 度 19 分）在 1777 年到2018 年。这些数据集是几个世纪以来使用早期雨量计和最近的 SIAP 翻斗模型收集的。通过研究元数据和对数据集的非参数测试，确定和分析了不均匀性的来源。在对仪器响应和定位特征的观测降雪数据进行校正后，获得了同质化的时间序列，用于在标准正态同质性测试的帮助下进行观测。进一步应用 Buishand 和 Mann-Kendall 检验来检查校正并检测可能的单调趋势。在研究期间，每年的降雪天数在 1897 年检测到的变化点之后减少，这与地表气温升高有关（包括明显的城市变暖趋势）。在这项研究中，在帕尔马 LIA 的最新阶段，每年大量的下雪天数（以下称为降雪频率）和雪深值与最小太阳活动周期一致，表明增强的、太阳诱导的阻挡活动占主导地位, 随着在西伯利亚和北欧发展的大型冷气团到达地中海。在上个世纪，雪似乎具有类似共振的特征，因为在北半球观察到类似的趋势，据报道，在春季和秋季过渡季节，积雪的范围显着下降。